In an extra-corporeal blood treating apparatus, such as a hemodialysis apparatus for example, the blood to be treated flows, in an extra-corporeal blood circuit, through the blood chamber of a dialyzer which is divided by a semi-permeable membrane into the blood chamber and a dialysis-fluid chamber, while in a dialysis-fluid system dialysis fluid flows through the dialysis-fluid chamber of the dialyzer. The extra-corporeal blood circuit has an arterial flexible line which runs to the blood chamber and a venous flexible line outgoing from the blood chamber. The flexible lines of the extra-corporeal blood treating apparatus are generally provided in the form of disposable items intended for once-only use. The known pieces of blood treating apparatus have a blood pump, which is usually arranged upstream of the blood chamber of the dialyzer, to ensure that there is an adequate flow of blood in the extra-corporeal blood circuit.
For highly efficient hemodialysis treatments, it is necessary for the blood to be cleansed from the patient to be fed to the extra-corporeal blood circuit at sufficiently high pumping rates. What is used for his purpose is preferably an operatively produced connection between artery and vein. Because of the bypassing of the peripheral vascular system, which presents a high resistance to flow, relatively high blow flows are obtained in the fistula or shunt, and these will be referred to in what follows as access flows. The extra-corporeal blood circuit is preferably connected up by means of two needles, with blood being withdrawn through the needle directed into the artery and being returned again through the needle directed into the vein after passing through the extra-corporeal blood circuit.
For different reasons, stenoses which result in a fall in the access flow may, in the course of time, form in the fistula or shunt. If the access flow is lower than the flow in the extra-corporeal blood circuit, this causes a drop in the cleansing performance because (venous) blood which is now already cleansed mixes with uncleansed (arterial) blood. This process is referred to as access recirculation. As well as by the fall in the access flow, the process may also be encouraged to occur by unfavorable positioning of the arterial and venous needles relative to one another.
By regular measurement of the access flow, it is intended that stenoses which are formed will be detected at an early stage, to enable steps to be taken to restore the access flow at an early point in time if the flow drops below a critical level.
Measurement of the access flow is possible by, for example, duplex sonography. This, however, calls for a trained physician and a cost-intensive diagnostic unit. Also, this method cannot be used with very adipose patients. What has become established as a standard method of determining access flow is the Krivitski method (Kidney Int (July) 48: 244-250 1995). In this, with the venous and arterial needles changed over, a bolus of saline solution is injected into the extra-corporeal blood tubing system and detected in the arterial and venous blood tubing lines by means of ultrasonic sensors. This method calls for an additional cost-intensive piece of equipment and for the manual administration of saline.
From European Patent Publication EP 0 928 614 B1 is known a method of determining access flow which does not call for any other measuring devices apart from the dialysis device and which manages without the manual injection of an indicator solution. In this case, clearance is determined, with constant blood and dialysis flows, with the needles in their normal arrangement and in a reversed arrangement in succession, and the access flow is determined from the two values for clearance.
For reversing the blood flow in the extra-corporeal blood circuit, there is known from PCT Publication No. WO 2006/042016 A2 a device which prevents a loss of blood which is possible when the needles are changed over, which reduces the risk of infection and simplifies operation. Also known is operator prompting implemented on the dialysis unit to allow an access flow measurement to be made by using the known device for flow reversal.
To determine access flow, measurements of clearance are made respectively before and after the reversal of blood flow in the extra-corporeal blood circuit. The operator prompting which is implemented on the dialysis unit tell the user when the reversal of flow is to be carried out. It is a disadvantage, however, that it is not automatically detected whether the reversal of flow has in fact taken place. If, incorrectly, there has not been a reversal of flow, the measurement may give too high a value for the access flow. This may result in problems at the vascular access not being realized, especially as the user will assume that he has made a correct measurement.
There is also the risk of the blood flow not being reversed back to its original direction after a measurement has been made with the blood flow reversed. Because of the increased access circulation which occurs when flow is reversed, this will then lead to a reduced dialysis dose.
For the automatic determination of the dialysis dose by the dialyzing unit, it is necessary for the current clearance to be known at all times during the treatment. For this purpose measurements arc made at different points in time. If there is a change in the parameters which affect clearance, and in particular in the blood and dialysate flows, between the measurements, interpolation is possible on the basis of the measurements which have been made and the known treatment parameters (German Patent Publication No. DE 19928407). Because the reversal of flow affects clearance, an exact knowledge of the length of time for which flow is reversed and of the duration of the treatment with the normal direction of flow is needed for determining the dialysis dose.
There is a technique which is known by the name radio frequency identification (RFID) which is in general use for the identification and location of articles. The articles are identified with the help of electromagnetic waves. An RFID system comprises a transponder which is situated on the article and a reader for reading the identity code of the transponder. The reader generates a short-range, high-frequency electromagnetic field by which, generally, not only can data be transmitted but the transponder can also be supplied with energy.
RFID transponders are known in different forms. All RFID transponders have an aerial which is connected to a transceiver. As well as the aerial and transceiver, what are also provided are a non-erasable memory and other circuits.
Known from Japanese Patent Application Publications JP 2233079 A2, JP 24232671 A2 and JP 2002333079 A2 are valves which have an RFID transponder to enable it to be detected whether the valve is open or closed. US Patent Application Publication No. 2007/0277824 A1 describes an apparatus intended for diagnostic purposes in which correct positioning of an insert is monitored by means of an RFID transponder.
The object underlying the present invention is to provide a device for reversing blood flow for an extra-corporeal blood treating apparatus, which device, with a high degree of safety and reliability, allows the safety of the extra-corporeal blood treatment to be increased and the measurement of parameters of the blood treatment to be simplified.
As well as this, the object underlying the present invention is also to specify a method of detecting the reversal of blood flow in extra-corporeal blood treatment which is easy to operate and can be safely and reliably applied.
A further object of the present invention is to provide a blood treating apparatus which, easily and with great safety and reliability, enables a reversal of flow to be made to enable parameters of the blood treatment to be measured.
These objects are achieved in accordance with the present invention by virtue of the features of the present invention set forth herein.